1. Field of the Invention
The present invention relates to a signal transfer circuit, a signal transfer apparatus, and a signal transfer method, and particularly to a signal transfer circuit that transfers a differential signal, a signal transfer apparatus including the signal transfer circuit, and a signal transfer method using the signal transfer circuit.
2. Description of Related Art
In the field of mobile terminals or the like, there are demands for reducing the number of necessary wires as much as possible in order to realize the miniaturization of devices. Therefore, the number of wires is reduced by serializing the parallel data. If data is serialized, the speed to transfer data must be increased. Thus the interface capable of high-speed communication by a differential signal is used. The differential signal is composed of a pair of complementary signals. One of the signals is set to a high level, and the other is set to a low level relative to a reference potential. Since a signal amplitude of the differential signal can be doubled as compared to when transferring one signal, the differential signal is used as a transmission signal in high-speed digital communication. On the other hand, the current consumption in high-speed communication continues to increase. Especially in the field of mobile terminals, the problem is to suppress the power consumption.
Therefore, there is a method under consideration that in the mode with a large amount of transfer data, a differential signal transmission is used, while in the mode with a small amount of transfer data, single-ended transmission that consumes little power and communicates with one transmission wire to transmit data is used.
The outline of the operation of switching the transmission mode in case two kinds of signals are supplied, which are a single-ended and a differential signals, is described with reference to FIG. 9.
FIG. 9 illustrates time T1, in which a single-ended signal is output in response to a CMOS signal input from two external terminals, and time T3 in which a differential signal is generated in response to two input signals. Further, the transmission is switched from the single-ended signal transmission to the differential signal transmission in time T2 by a received voltage level switch signal. Either a high or low level value is set to the voltage level. Blanking time is provided in which a low level value is set to both of the two input signals and a differential signals is received. In the blanking time, there is no voltage difference between the two input signals. The time T2 and the blanking time indicate the same period.
Further, Japanese Unexamined Patent Application Publication No. 2008-113196 discloses a signal detection circuit that detects a differential signal with a minute amplitude. Specifically, the signal detection circuit can determine that no-signal state generated by an abnormal state of a data transmission path is different from the state in which there is a signal having a minute amplitude generated at the time of differential signal transmission. When the signal detection circuit determines that it is the no-signal state, an abnormal detection process is performed.